1. Field of the Invention
This invention relates to tin alloys and, more particularly, to tin alloys that contain small amounts of certain elements.
2. Description of the Prior Art
It has long been known that the oxidation resistance of tin can be improved by the addition of small amounts (about 0.1 at. %) of certain alloying elements that exhibit appreciable solid solubility in tin (W. E. Boggs et al., J. Electrochem. Soc. 110, 4 (1963)). More recently, the effect of certain impurity elements on the wetting properties of tin-lead solders was reported (M. L. Ackroyd et al., Metals Technology, February, 1975, p. 73).
A tin-based solder system for attaching semiconductor devices to a metal package was discussed in U.S. Pat. No. 4,170,472, issued Oct. 9, 1979, to Olsen et al.
During the past decade, several publications have appeared that describe progress in the development of rapidly solidified filler metal alloy foils (See, e.g., N.J DeCristofaro et al., Welding Journal 57(7), 33 (1978); D. Bose et al., Welding Journal 60(10), 29 (1981); and A. Datta et al., Welding Journal 63(10), 14 (1984)).
Nevertheless, tin-based alloys generally suffer discoloration on melting. This discoloration results from oxidation of the tin and, for filler metal alloys, is associated with poor performance (e.g., dewetting of substrates by molten solder and premature failure of devices).